Just been doing some EMQs and the question below came up about x-linked inheritance. I think this question will confuse people, unless I am mistaken. It states that the father has a condition and that the brother does too. If this condition was x-linked then by definition the brother/son would not have the condition (unless the mother was also a carrier). However, the answer says it is x-linked recessive. Any thoughts or am I getting the wrong end of the stick. Personally I wasn't sure if any of the answers would be right from the information we were given.
Options for Questions 5-5
A
Autosomal dominant
B
Autosomal recessive
C
X-linked recessive
D
X-linked dominant
E
Autosomal dominant with incomplete penetrance
F
Autosomal dominant with variable expressivity
G
Polygeneic transmission
H
Confined placental mosaicism
I
Non-mendelian inheritance
J
Inheritance through mitochondrial DNA
K
X-linked recessive with lyonisation
L
X-linked dominant with lyonisation
Instructions:For each of the case histories described below, choose the single most likely mode of inheritance from the above list of options. Each option may be used once, more than once, or not at all.
Question 5
A 25 year old woman has been referred for pre-natal diagnosis. Her father and brother suffer from an inherited condition. She is found to be carrying a female fetus and has been reassured.
Posted by Farrukh G.
x-linked inheritance
Posted by Jonathan N. Tue Feb 4, 2014 02:44 pm
Just been doing some EMQs and the question below came up about x-linked inheritance. I think this question will confuse people, unless I am mistaken. It states that the father has a condition and that the brother does too. If this condition was x-linked then by definition the brother/son would not have the condition (unless the mother was also a carrier). However, the answer says it is x-linked recessive. Any thoughts or am I getting the wrong end of the stick. Personally I wasn't sure if any of the answers would be right from the information we were given.
You have descibed the circumstances where this would be possible. The question goes on to make the answer even more obvious: she if found to have a female fetus and has been reassured. Why will they reassure her on this basis UNLESS the condition was X-linked?
Posted by Jonathan N.
I agree with your point that she is reassured by the female fetus and so this is clearly the answer. Obviously my/our genetics knowledge tends to be better at the more simple inheritance patterns, so obviously the father having the disease is a red herring. Generally though I have been taught to keep genetic scenarios simple and the likelihood of a mother being a carrier and the father having the condition is small (a haematologist told us there are only 7 families in the country where this is the case with haemophilia).
